Mobil 1 will be fine, but I don't really care for Valvoline products. Keep in mind that if you replace the diff fluid, you will want to order two new aluminum crush washers (from the dealer or online, but they have to be OEM BMW parts), and you'll need to get your hands on (or make) a stubby hex tool to get the diff fill plug out (clearance is an issue, since the spare tire well is in the way - a standard hex tool will not fit). You'll also want a long breaker bar, since the plugs on the trans & diff can be on there pretty good.